Many of today's devices use lasers to implement various functions. For example, an optical mouse or laser pointer use lasers in their respective operations. Additionally, many fiber-optic communication devices use a laser as a source of signal generation.
These lasers generate optical beams that can sometimes generate light powerful enough to damage the human eye. For example, a laser-optic pointing device typically includes a beam-modifying apparatus in optical alignment with the laser designed to focus or collimate the laser beam for its intended use. Therefore, if a person looks into the laser beam, it may cause damage to the unaided eye. And even if the laser beam is not powerful enough to cause eye damage, one may further focus the laser beam with a magnifying lens or other optical instrument such that the further focused beam is capable of causing damage to the eye.
Because products containing laser devices are potentially hazardous to the eye, they are classified accordingly by their potential hazard level. One such classification scheme is the International Standards for The Safety of Laser Products (ISSLP). The least hazardous laser devices, as classified by the ISSLP, are classified as Class 1 laser devices. Laser devices in this category are defined as being safe under reasonably foreseeable—although perhaps not recommended—conditions of use, such as the use of optical instruments such as a magnifying lens for intra-beam viewing. The classification for the next-least-hazardous category of laser devices is Class 1M. This classification covers laser devices that are safe under reasonably foreseeable conditions of operation, but may be hazardous if the user employs an optical instrument such as a magnifying lens for intra-beam viewing.
According to the ISSLP, the maximum-allowed power, i.e., acceptable emission light (AEL) level, for a commonly used single-mode 850 nanometer (nm) wavelength Class 1 laser device is 0.78 milliwatts (mW) when measured according to the ISSLP-defined standard. The defined standard is the amount of flux (power per unit area) through a 7 millimeter (mm) aperture in a radial plane that is 14 mm from the point where the laser beam exits the device. Thus, if the flux of the laser beam that passes through the 7 mm aperture is less than 0.78 mW, then the laser device is considered Class 1 safe.
A speckle-based motion sensor, which could be used in an optical mouse, is a device that uses a laser for its functionality. In a speckle-based motion sensor, a laser beam is directed to a surface and the reflection of the laser beam from the surface creates a complex diffraction pattern, called a speckle pattern. If the laser beam moves relative to the surface, then the speckle pattern changes. Detectors for receiving the reflected speckle pattern can then determine the relative changes in the speckle pattern and translate these changes into the relative lateral motion of the laser-beam source. For acceptable performance, however, a laser in a speckle-based motion sensor is typically operated at power levels that exceed the maximum-allowable AEL for a Class 1 rating. That is, if the power is reduced to meet the Class 1 requirements, the speckle-based motion sensor may not perform at an acceptable level.